Quantcast

My first rocket design in OpenRocket

The Rocketry Forum

Help Support The Rocketry Forum:

MetricRocketeer

Well-Known Member
TRF Supporter
Joined
Jun 1, 2018
Messages
257
Reaction score
42
Hi everyone,

OK. So the tail ring does contribute aerodynamically. But it also protects the fins. Isn't that true?

I wasn't quite ready to introduce this. In light of the current discussion, however, I will do so now. It is the first rocket that I designed using OpenRocket. A few of the components are taken directly from a copy of the OpenRocket file for the LOC/Precision Doorknob. Nevertheless, the overall design is mine, and I call it The Needle. I still have some details to work out. For this rocket, the tail ring also protects the fins, I think.

Incidentally, I don't know how to show just the picture of 3D Finished, so I am uploading the file.

Also, incidentally, now that I am learning the program, I really love OpenRocket for rocket design.

Stanley
 

Attachments

MetricRocketeer

Well-Known Member
TRF Supporter
Joined
Jun 1, 2018
Messages
257
Reaction score
42
Hi everyone,

In case anyone may be interested, here is my first rocket design that I made with OpenRocket. I call the rocket The Needle.

Stanley
1613333442711.png

1613333520662.png
 

K'Tesh

OpenRocket Chuck Norris
TRF Supporter
Joined
Mar 27, 2013
Messages
14,782
Reaction score
1,231
Interesting... What diameter motor are you thinking?
 

MetricRocketeer

Well-Known Member
TRF Supporter
Joined
Jun 1, 2018
Messages
257
Reaction score
42
Hi K'Tesh,

I built it using the Modular Motor Adapter System (MMAS, as I am sure you know). I used the 54 mm motor mount, but I could have used anything.

I have only simmed it with 54 mm motors, but I could experiment with lower-diameter ones as well.

Stanley
 
Last edited:

neil_w

Marginally Stable
TRF Supporter
Joined
Jul 14, 2015
Messages
11,013
Reaction score
3,867
Location
Northern NJ
How big is that ring? I always wonder how very large rings are to be fabricated. Mine was 5" on Alcubierre, but it was balsa and I don't think I'd fly a balsa ring on a rocket with a 54mm mount.
 

MetricRocketeer

Well-Known Member
TRF Supporter
Joined
Jun 1, 2018
Messages
257
Reaction score
42
Hi neil_w,

I built it using a centering ring with these dimensions: outer diameter = 59.9 cm; inner diameter = 59.5 cm; thickness = 12 cm.

Actually, we had quite a spirited discussion about two issues -- how to build it in OpenRocket (I using a centering ring and K'Tesh used an externalized internal body tube) and the fact that OR does not actually represent the item in simulations.

I would like to know how much the tail ring contributes to flight stability. In any event, it seems to me that a tail ring protects the fins.

I have so many questions about the tail ring that I am having trouble concentrating my focus. But I would hope that it does protect the fins. What do people think -- would the tail ring protect the fins?

Stanley
 

K'Tesh

OpenRocket Chuck Norris
TRF Supporter
Joined
Mar 27, 2013
Messages
14,782
Reaction score
1,231
Hi neil_w,

I built it using a centering ring with these dimensions: outer diameter = 59.9 cm; inner diameter = 59.5 cm; thickness = 12 cm.

Actually, we had quite a spirited discussion about two issues -- how to build it in OpenRocket (I using a centering ring and K'Tesh used an externalized internal body tube) and the fact that OR does not actually represent the item in simulations.

I would like to know how much the tail ring contributes to flight stability. In any event, it seems to me that a tail ring protects the fins.

I have so many questions about the tail ring that I am having trouble concentrating my focus. But I would hope that it does protect the fins. What do people think -- would the tail ring protect the fins?

Stanley
Generally, we'd refer to what you called thickness as "length". Thickness in OR is one half the difference between OD and ID.
 

MetricRocketeer

Well-Known Member
TRF Supporter
Joined
Jun 1, 2018
Messages
257
Reaction score
42
Generally, we'd refer to what you called thickness as "length". Thickness in OR is one half the difference between OD and ID.
Hi K'Tesh,

You are far more knowledgeable about OpenRocket than I am. On this issue, however, I think that you are mistaken because 59.9 cm minus 59.5 cm equals 0.4 cm. And the length -- which would be a better term -- does indeed equal 12 cm.

Stanley
 

MetricRocketeer

Well-Known Member
TRF Supporter
Joined
Jun 1, 2018
Messages
257
Reaction score
42
Yep, makes the entire fin can more durable. I was goofing around on a design today and added a ring for that very purpose.

View attachment 450677
If lakeroadster is indeed correct -- and it seems to me he is -- then more rockets should use them. As we all know, fins are so vulnerable to damage. Of course the ring tail adds weight, which may or may not be a problem.
 

MetricRocketeer

Well-Known Member
TRF Supporter
Joined
Jun 1, 2018
Messages
257
Reaction score
42
Now here's a question. How would you actually attach the ring tail? You would have to push it making a snug fit on the top of each fin. Also, you would need to epoxy the ring tail at the top of each fin. I guess this could all be done, but it is more than a minor detail of which we cannot lose sight.
 

neil_w

Marginally Stable
TRF Supporter
Joined
Jul 14, 2015
Messages
11,013
Reaction score
3,867
Location
Northern NJ
If lakeroadster is indeed correct -- and it seems to me he is -- then more rockets should use them. As we all know, fins are so vulnerable to damage. Of course the ring tail adds weight, which may or may not be a problem.
  1. The ring adds tail weight
  2. The ring adds quite a bit of drag
  3. "Protecting the fins" per se is not a high priority for most builders. Normally, fins with some combination of short span, long root, and sweep forward from the bottom are not prone to damage.
  4. Not everyone digs the look
  5. Rings can be hard to fabricate at large sizes
Now here's a question. How would you actually attach the ring tail? You would have to push it making a snug fit on the top of each fin. Also, you would need to epoxy the ring tail at the top of each fin. I guess this could all be done, but it is more than a minor detail of which we cannot lose sight.
If the ring is all the way outside the fins, then yeah, you slip it over and glue (sometimes after painting, because painting the inside of the ring can be a pain). If the fins extend beyond the ring then slots may be cut in the ring and/or the fins to get a good secure interlocking fit.

If the fins are hand-cut, then getting a precise fit of a ring can be a non-trivial challenge, at least in my experience so far.
 

K'Tesh

OpenRocket Chuck Norris
TRF Supporter
Joined
Mar 27, 2013
Messages
14,782
Reaction score
1,231
Hi K'Tesh,

You are far more knowledgeable about OpenRocket than I am. On this issue, however, I think that you are mistaken because 59.9 cm minus 59.5 cm equals 0.4 cm. And the length -- which would be a better term -- does indeed equal 12 cm.

Stanley
Oh, I doubt I'm mistaken... Check out this "ring fin" from the Lil' Augie. Wall thickness: 0.045", Length 8".

OD (2.84") - ID (2.75") = 0.09.
Now take that 0.09"/2 = Wall thickness 0.045"

1613350994786.png
 
Last edited:

Neutron95

Well-Known Member
TRF Supporter
Joined
Jan 17, 2010
Messages
301
Reaction score
134
This is a great first design. It is certainly more detailed than anything I've ever designed in Openrocket before. However there are a few things that could be improved on.

First off is the ring fin. As far as I know, the current release of Openrocket doesn't simulate them. You can make things that look like ring fins with various internal tubes, or centering rings, as you've done here. However, Openrocket will not take them into account when it determines the aerodynamics of the rocket. Openrocket only calculates aerodynamic effects for nosecones, transitions, body tubes, and fins. I moved the ring fin to a separate stage, so you can toggle it on and off, and see that the CP doesn't move. Fortunately, you've designed a stable rocket, and I don't see the fin reducing that; it will just cause the rocket to have a lot more drag in real life than in the sims.

If you're planning on building this, I have a few other suggestions. The rail guides are really far forward. My general rule of thumb is to have one near the CG, and then have another one close to the base of the rocket. You lose a lot of guidance once the first guide clears the rail, so this maximizes the effective length of the rail. I'd also adjust the fin shape so that there is a flat tip where they meet the ring fin, just to get a stronger joint there. I don't know what manufacturing skills you have, but I would suggest using commercially available parts for the nosecone and transition to make your life easier. I'd also suggest a larger motor mount, but that is just personal preference :).

Overall, I think it's a really neat design, and with a few tweaks it should be a good flyer.
 

Attachments

MetricRocketeer

Well-Known Member
TRF Supporter
Joined
Jun 1, 2018
Messages
257
Reaction score
42
Oh, I doubt I'm mistaken... Check out this "ring fin" from the Lil' Augie. Wall thickness: 0.045", Length 8".

OD (2.84") - ID (2.75") = 0.09.
Now take that 0.09"/2 = Wall thickness 0.045"

View attachment 450691
1613362872051.png


Hi K'Tesh,

Thank you for your response.

But the dialog box for your ring tail differs from my dialog box. Notice that your dialog box shows "Wall thickness" and "Length," whereas mine shows only "Thickness."

I guess this results from the fact that your ring tail is made from an inner tube, whereas my ring tail is made from a centering ring.

Stanley
 

MetricRocketeer

Well-Known Member
TRF Supporter
Joined
Jun 1, 2018
Messages
257
Reaction score
42
  1. The ring adds tail weight
  2. The ring adds quite a bit of drag
  3. "Protecting the fins" per se is not a high priority for most builders. Normally, fins with some combination of short span, long root, and sweep forward from the bottom are not prone to damage.
  4. Not everyone digs the look
  5. Rings can be hard to fabricate at large sizes
Hi neil-w,

You make great points, which definitely provide food for thought.

Stanley
 

MetricRocketeer

Well-Known Member
TRF Supporter
Joined
Jun 1, 2018
Messages
257
Reaction score
42
This is a great first design. It is certainly more detailed than anything I've ever designed in Openrocket before. However there are a few things that could be improved on.

First off is the ring fin. As far as I know, the current release of Openrocket doesn't simulate them. You can make things that look like ring fins with various internal tubes, or centering rings, as you've done here. However, Openrocket will not take them into account when it determines the aerodynamics of the rocket. Openrocket only calculates aerodynamic effects for nosecones, transitions, body tubes, and fins. I moved the ring fin to a separate stage, so you can toggle it on and off, and see that the CP doesn't move. Fortunately, you've designed a stable rocket, and I don't see the fin reducing that; it will just cause the rocket to have a lot more drag in real life than in the sims.

If you're planning on building this, I have a few other suggestions. The rail guides are really far forward. My general rule of thumb is to have one near the CG, and then have another one close to the base of the rocket. You lose a lot of guidance once the first guide clears the rail, so this maximizes the effective length of the rail. I'd also adjust the fin shape so that there is a flat tip where they meet the ring fin, just to get a stronger joint there. I don't know what manufacturing skills you have, but I would suggest using commercially available parts for the nosecone and transition to make your life easier. I'd also suggest a larger motor mount, but that is just personal preference :).

Overall, I think it's a really neat design, and with a few tweaks it should be a good flyer.
Hi Neutron 95,

Thank you so much for this excellent contribution.

• I particularly enjoyed how you moved the ring fin to a separate stage to analyze its effect on the rocket's CP. That was a clever idea.

• I will definitely adjust the positions of the rail guides.

• Good idea about flattering the top of the fins to make a stronger joint. I will work on that.

• As for the nosecone, I did use a LOC PNC-5.38L from the database. Actually, for the two body tubes and for the transition, I wanted to use something from the database. However, even though I found items whose published dimensions matched what I needed, OR gave me an error message about body-tube discontinuity. I don't understand why that happened, and I wish I did understand it.

Stanley
 

MetricRocketeer

Well-Known Member
TRF Supporter
Joined
Jun 1, 2018
Messages
257
Reaction score
42
Hi Neutron95 and anyone else,

I tried to run the simulations with the stage. But they didn't run because, as soon as I had a second stage in place, whether or not I activated it, the configuration was J210-6 (or whatever the motor was) followed by none. Thus, the motor didn't ignite.

Please, how do I get around this issue?

Thank you.

Stanley
 

Neutron95

Well-Known Member
TRF Supporter
Joined
Jan 17, 2010
Messages
301
Reaction score
134
However, even though I found items whose published dimensions matched what I needed, OR gave me an error message about body-tube discontinuity. I don't understand why that happened, and I wish I did understand it.
I've had that happen on a few of my designs, where the cone and body tube were slightly different sizes. I've heard of it happening on parts where the OD does match up though. I usually ignore it, my sims don't seem to be too inaccurate.

For your simulation problem, the easiest thing to do would be to just put the ring back where it was. I just did that to show that it wasn't affecting the CP, not for any simulations.
 

K'Tesh

OpenRocket Chuck Norris
TRF Supporter
Joined
Mar 27, 2013
Messages
14,782
Reaction score
1,231
View attachment 450702

Hi K'Tesh,

Thank you for your response.

But the dialog box for your ring tail differs from my dialog box. Notice that your dialog box shows "Wall thickness" and "Length," whereas mine shows only "Thickness."

I guess this results from the fact that your ring tail is made from an inner tube, whereas my ring tail is made from a centering ring.

Stanley
We both learned something today. Thanks for sharing that.
 

Mike Haberer

Well-Known Member
TRF Supporter
Joined
Jan 7, 2019
Messages
434
Reaction score
273
Hi neil_w,

I built it using a centering ring with these dimensions: outer diameter = 59.9 cm; inner diameter = 59.5 cm; thickness = 12 cm.

Actually, we had quite a spirited discussion about two issues -- how to build it in OpenRocket (I using a centering ring and K'Tesh used an externalized internal body tube) and the fact that OR does not actually represent the item in simulations.

I would like to know how much the tail ring contributes to flight stability. In any event, it seems to me that a tail ring protects the fins.

I have so many questions about the tail ring that I am having trouble concentrating my focus. But I would hope that it does protect the fins. What do people think -- would the tail ring protect the fins?

Stanley
12cm is one thick ring...and 60 cm = 24 inches. You'll need a much bigger MMT. I think you meant mm (LOL)...
 

JoePfeiffer

Well-Known Member
Joined
Jun 15, 2013
Messages
165
Reaction score
137
Generally, we'd refer to what you called thickness as "length". Thickness in OR is one half the difference between OD and ID.
He's modeling the fin ring as a very strange (I don't think he'll object to my characterizing it as such!) centering ring. "Thickness" is indeed the correct term here.

I'd suggest modeling it as a very large "internal" tube, as that comes closer to showing his intent. As others have said, only the weight and not the aero will be modeled in either case, and I'd expect the weight estimate to be the same.
 

Mike Haberer

Well-Known Member
TRF Supporter
Joined
Jan 7, 2019
Messages
434
Reaction score
273
Has anyone ever simmed something like this in both Rocksim and OpenRocket to see if they handle the ring (which is essentially a tube fin) differently? Rocksim handles tube fins natively....
 

neil_w

Marginally Stable
TRF Supporter
Joined
Jul 14, 2015
Messages
11,013
Reaction score
3,867
Location
Northern NJ
Has anyone ever simmed something like this in both Rocksim and OpenRocket to see if they handle the ring (which is essentially a tube fin) differently? Rocksim handles tube fins natively....
Rocksim has native tail ring, so it is definitely different.

Tube fins should be similar; if I get a chance I'll do a little comparison between them.
 

neil_w

Marginally Stable
TRF Supporter
Joined
Jul 14, 2015
Messages
11,013
Reaction score
3,867
Location
Northern NJ
Tube fins should be similar; if I get a chance I'll do a little comparison between them.
Well that is not too encouraging. Rocksim on top, OR on bottom: design is a nose cone, 18" BT50, and set of 6 3" BT20 tube fins:
1613435944207.png

Rocksim reports CP at 16.95", OR at 18.54". Frankly, the OR numbers seem more sensible to me, but I dunno.
 

MetricRocketeer

Well-Known Member
TRF Supporter
Joined
Jun 1, 2018
Messages
257
Reaction score
42
Hi neil_w and everyone,

Aren't those two results -- in RS and in OR -- very roughly comparable?

Stanley
 

Latest posts

Top